Immunocytochemical localization of gonadotropin-releasing hormone (Gn-RH) and antidiuretic hormone (ADH) will be done at both the light and electron microscopic level in the hypothalamus and median eminence at different stages of the estrous cycle in rats and sheep. Content of ADH and Gn-RH will be determined by radioimmunoassay in specific hypothalamic regions, cerebrospinal fluid, and serum for correlation of results with localization studies. In order to enhance hormone content in processes of arcuate nucleus neurosecretory neurons, and establish their projection on the median eminence, immunoperoxidase studies will be done on animals that are castrated and/or administered colchicine. Also, the immunoperoxidase method will be used to visualize: terminals from the supraoptic nucleus on hypophysial portal vessels; neurohormones in tanycytes and circumventricular organs; and other structures implicated in the passage of releasing hormones to the hypophysis via a ventricular route. Intraventricular infusion of Gn-RH and ADH will be used to enhance visualization of hormones in the tanycyte perikarya and their processes. Thus, our objectives are to determine the sites of synthesis, mode of transport, and sites of release of Gn-RH and ADH, and to investigate any possible role ADH has in the release of luteinizing hormone. BIBLIOGRAPHIC REFERENCES: Scott, D. E., J. R. Sladek, Jr., G. P. Kozlowski, T. H. McNeill, W. K. Paull and G. Krobisch-Dudley. The median eminence as a neuroendocrine transducer. In: Neuroendocrine Regulation of Fertility. Ed. T. C. Anand-Kumar, S. Karger, Basel, 1976, pp. 57-70. Kozlowski, G. P., M. S. Brownfield and W. J. Schultz. Neurosecretory pathways to the choroid plexus. Int. Res. Comm. Sys. 4:299, 1976.